8.2 - Blood Vessels Flashcards
How extensive is the human circulatory system?
If all blood vessels in an adult human were laid end to end, they would stretch 100,000 miles, roughly four times around the Earth.
Why is the circulatory system in humans considered typical of mammals?
It follows the double closed circulatory system, allowing efficient oxygen and nutrient transport to sustain high metabolic demands.
What is the relationship between blood vessel structure and function?
Blood vessels have specialized components (elastic fibers, smooth muscle, and collagen) that allow them to withstand pressure, control blood flow, and provide structural integrity.
What are the three types of tissues utilised in blood vessels?
- Elastic Fibres
- Smooth Muscle
- Collagen
What are elastic fibers, and what is their role in blood vessels?
Elastic fibers are made of elastin, allowing blood vessels to stretch when blood is pumped through them and recoil to maintain blood pressure. They are especially important in arteries that experience high pressure.
How does smooth muscle contribute to blood vessel function?
Smooth muscle contracts and relaxes, controlling the lumen size (the internal channel of the blood vessel). This helps regulate blood pressure and flow, ensuring efficient circulation.
What is the function of collagen in blood vessels?
Collagen provides structural support, maintaining the shape and volume of blood vessels, preventing overstretching or rupture under pressure.
Why is flexibility important in blood vessels?
Blood vessels must be flexible to accommodate changes in blood pressure and volume while maintaining efficient circulation without damage.
How do different blood vessels vary in their composition?
The presence of elastic fibers, smooth muscle, and collagen varies between arteries, veins, and capillaries, depending on their function and pressure requirements.
What is the function of arteries?
Arteries carry blood away from the heart to the tissues of the body. They typically carry oxygenated blood, except for the pulmonary artery (to the lungs) and the umbilical artery (from fetus to placenta).
What is the exception to the normal role of arteries?
- Pulmonary artery which carries deoxygenated blood from the heart to the lungs
- During pregnancy, the umbilical artery which carries oxygenated blood from the fetus to the placenta.
Why is blood in the arteries under high pressure?
Arteries receive blood directly from the heart, which pumps it forcefully, requiring arteries to have thick, elastic walls to withstand the high pressure.
What key structural components are found in artery walls, and what are their functions?
- Elastic fibers – allow arteries to stretch and recoil, maintaining blood flow.
- Smooth muscle – controls lumen size, regulating blood pressure.
- Collagen – provides structural support, preventing overstretching.
How do elastic fibers help maintain blood flow in arteries?
Elastic fibers stretch when blood is pumped from the heart and recoil between heartbeats. This evens out blood pressure but does not completely eliminate pulsation, which is why a pulse can still be felt.
What is the endothelium, and why is it important in arteries?
The endothelium is the smooth inner lining of the artery, allowing blood to flow easily with minimal friction, reducing resistance.
What are arterioles, and how do they differ from arteries?
Arterioles are smaller blood vessels that link arteries to capillaries. They have more smooth muscle and less elastic fiber than arteries, as they experience less pulsation but control blood flow to tissues.
How do arterioles regulate blood flow to organs?
Arterioles can constrict (vasoconstriction) or dilate (vasodilation) using their smooth muscle, controlling how much blood enters capillary beds.
What is vasoconstriction, and why is it important?
Vasoconstriction is when the smooth muscle in the arteriole contracts, narrowing the vessel and reducing blood flow to capillaries, helping regulate blood distribution and pressure.
What is vasodilation, and how does it affect blood flow?
Vasodilation is when the smooth muscle in the arteriole relaxes, widening the vessel and increasing blood flow to capillaries, ensuring organs get the oxygen they need.
What is an aneurysm?
An aneurysm is a bulge or weakness in a blood vessel wall, most commonly occurring in the aorta or brain arteries.
Why are aneurysms dangerous?
Most aneurysms go undetected until they burst, which can lead to severe internal bleeding and can be fatal.
What is one major risk factor for aneurysms?
High blood pressure increases the risk of aneurysm formation by putting extra strain on blood vessel walls.
How does the ratio of collagen to elastin change in aneurysms?
In a healthy aorta, the collagen:elastin ratio is 1.85:1. As aneurysms develop, this ratio increases, indicating more collagen and less elastin, reducing flexibility.
How does the collagen:elastin ratio change as an aneurysm enlarges?
Normal aorta: 1.85:1
Small aneurysm: 3.75:1
Large aneurysm: 7.9:1
This suggests that an imbalance in collagen and elastin may contribute to aneurysm formation.
Why is elastin important in blood vessel walls?
Elastin allows blood vessels to stretch and recoil, maintaining blood flow and pressure regulation.
Why might an increased collagen:elastin ratio lead to aneurysms?
Too much collagen makes the vessel stiff and less elastic, so it cannot recoil properly after stretching, increasing the risk of aneurysm formation.
How is research helping prevent aneurysm-related deaths?
Scientists are studying the collagen:elastin ratio to see if it can predict aneurysm risk, potentially leading to regular aortic screening for early detection.
What are capillaries, and what is their function?
Capillaries are microscopic blood vessels that link arterioles to venules. They form a dense network throughout body tissues, allowing the exchange of substances between the blood and tissue cells.
How small are capillaries, and how does this affect blood flow?
Capillaries have an extremely narrow lumen, forcing red blood cells (7.5-8 µm in diameter) to pass through in single file, slowing down blood flow and facilitating efficient diffusion.
How do substances pass between capillaries and surrounding tissues?
In most capillaries, there are gaps between endothelial cells where substances can pass into surrounding tissue fluid. However, in the central nervous system, tight junctions prevent this, forming the blood-brain barrier.
How does blood composition change as it passes through capillaries? What are the exceptions?
In most organs, oxygenated blood enters the capillaries, and by the time it leaves through venules, it is deoxygenated.
Exceptions: In the lungs and placenta, deoxygenated blood enters the capillaries and leaves oxygenated.
What are the three ways that capillaries are adapted for their role?
- They provide a very large surface area for the diffusion of substances into an out of the cell
- The total cross sectional area of the capillaries is always greater than the arteriole supplying them so the rate of blood flow Falls. The relatively slow movement of blood through capillaries gives more time for the exchange of materials by diffusion between the blood and the cells
- The walls are a single endothelial cell thick giving a very thin layer for diffusion
Why is the total cross-sectional area of capillaries important?
The total cross-sectional area of capillaries is greater than that of the arteriole supplying them, causing blood flow to slow down, allowing more time for diffusion.
How does the structure of capillary walls aid diffusion?
Capillary walls are only one endothelial cell thick, providing a very thin diffusion pathway, making exchange of substances highly efficient.
What is the function of veins in the circulatory system?
Veins carry blood back to the heart from the body’s cells, mostly transporting deoxygenated blood, except for the pulmonary vein and umbilical vein.
What are the two exceptions where veins carry oxygenated blood?
- Pulmonary vein – carries oxygenated blood from the lungs to the heart.
- Umbilical vein – carries oxygenated blood from the placenta to the fetus during pregnancy.
How does deoxygenated blood return to the heart?
Capillaries → Venules → Larger veins
Blood then flows into the two major veins:
1. Superior vena cava (from head and upper body).
2. Inferior vena cava (from lower body).
Why don’t veins have a pulse?
The pulses from the heart are lost when blood passes through narrow capillaries, so veins do not experience the same surges of pressure as arteries.
What role do veins play as a blood reservoir?
Veins can hold up to 60% of total blood volume at any time, acting as a blood reservoir due to their large lumen and lower pressure.
Why is blood pressure lower in veins compared to arteries?
Blood pressure in veins is much lower because the heart’s pumping force has dissipated after passing through capillaries.
What structural adaptations help veins return blood to the heart?
- Valves – Prevent backflow of blood, ensuring it moves in one direction.
- Wide lumen – Reduces resistance to blood flow.
- Smooth endothelium – Ensures blood flows easily.
How are venules different from veins?
- Venules link capillaries to veins.
- They have very thin walls with little smooth muscle.
- Several venules join together to form larger veins.
Why does deoxygenated blood in veins need assistance to return to the heart?
Blood in veins is under low pressure and often must move against gravity to return to the heart for oxygenation in the lungs.
What are the three main adaptations that help venous return?
- One-way valves
- Skeletal muscle contractions
- Breathing movements of the chest
How do one-way valves in veins assist in blood flow?
- Valves are folds in the inner lining of veins.
- They open when blood moves towards the heart.
- If blood tries to flow backwards, the valves close, preventing backflow.
How does skeletal muscle contraction help push blood towards the heart?
- Large veins run between active muscles (e.g., in legs and arms).
- When muscles contract, they squeeze the veins, pushing blood towards the heart.
- Valves prevent backflow when the muscles relax.
How do breathing movements of the chest aid venous return?
- Pressure changes during inhalation and exhalation create a pumping effect.
- This squeezes veins in the chest and abdomen, helping move blood towards the heart.
Why is the combination of the three mechanisms that help deoxygenated blood return to the heart important?
Together, valves, muscle contractions, and breathing movements ensure efficient return of deoxygenated blood to the heart, preventing blood pooling and maintaining circulation.
